From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1076DC4360C for ; Wed, 16 Oct 2019 10:25:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2AEC20650 for ; Wed, 16 Oct 2019 10:25:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392407AbfJPKZx (ORCPT ); Wed, 16 Oct 2019 06:25:53 -0400 Received: from foss.arm.com ([217.140.110.172]:35270 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730972AbfJPKZx (ORCPT ); Wed, 16 Oct 2019 06:25:53 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BA6CB28; Wed, 16 Oct 2019 03:25:52 -0700 (PDT) Received: from bogus (unknown [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D936C3F6C4; Wed, 16 Oct 2019 03:25:50 -0700 (PDT) Date: Wed, 16 Oct 2019 11:25:45 +0100 From: Sudeep Holla To: Yunfeng Ye Cc: Will Deacon , David Laight , "catalin.marinas@arm.com" , "kstewart@linuxfoundation.org" , "gregkh@linuxfoundation.org" , "ard.biesheuvel@linaro.org" , "tglx@linutronix.de" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "wuyun.wu@huawei.com" , hushiyuan@huawei.com, linfeilong@huawei.com Subject: Re: [PATCH V2] arm64: psci: Reduce waiting time of cpu_psci_cpu_kill() Message-ID: <20191016102545.GA11386@bogus> References: <18068756-0f39-6388-3290-cf03746e767d@huawei.com> <20191015162358.bt5rffidkv2j4xqb@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 16, 2019 at 11:22:23AM +0800, Yunfeng Ye wrote: > > > On 2019/10/16 0:23, Will Deacon wrote: > > Hi, > > > > On Sat, Sep 21, 2019 at 07:21:17PM +0800, Yunfeng Ye wrote: > >> If psci_ops.affinity_info() fails, it will sleep 10ms, which will not > >> take so long in the right case. Use usleep_range() instead of msleep(), > >> reduce the waiting time, and give a chance to busy wait before sleep. > > > > Can you elaborate on "the right case" please? It's not clear to me > > exactly what problem you're solving here. > > > The situation is that when the power is off, we have a battery to save some > information, but the battery power is limited, so we reduce the power consumption > by turning off the cores, and need fastly to complete the core shutdown. However, the > time of cpu_psci_cpu_kill() will take 10ms. We have tested the time that it does not > need 10ms, and most case is about 50us-500us. if we reduce the time of cpu_psci_cpu_kill(), > we can reduce 10% - 30% of the total time. > Have you checked why PSCI AFFINITY_INFO not returning LEVEL_OFF quickly then ? We wait for upto 5s in cpu_wait_death(worst case) before cpu_kill is called from __cpu_die. Moreover I don't understand the argument here. The cpu being killed will be OFF, as soon as it can and firmware controls that and this change is not related to CPU_OFF. And this CPU calling cpu_kill can sleep and 10ms is good to enter idle states if it's idle saving power, so I fail to map the power saving you mention above. > So change msleep (10) to usleep_range() to reduce the waiting time. In addition, > we don't want to be scheduled during the sleeping time, some threads may take a > long time and don't give up the CPU, which affects the time of core shutdown, > Therefore, we add a chance to busy-wait max 1ms. > On the other hand, usleep_range reduces the timer interval and hence increases the chance of the callee CPU not to enter deeper idle states. What am I missing here ? What's the use case or power off situation you are talking about above ? > > > I've also added Sudeep to the thread, since I'd like his ack on the change. > > Thanks Will. -- Regards, Sudeep